This invention relates to a system for arctic seafloor reconnaissance and a method of using such a system to collect imagery and depth data. More particularly, this invention relates to a relatively lightweight system for collecting high quality sonar data on topographic features of arctic seafloor and a method of using such a system.
In the Arctic, bottom-founded structures of all types require a site-specific investigation to determine hazards, bathymetry, and soil characteristics, but the sea is predominantly covered by permanent pack ice in an environment of extremes with ambient temperatures ranging from -70.degree. F. in the winter to 80.degree. F. in the brief summer period. During the short summer, a narrow window of open water opportunity may allow conventional methods of seafloor reconnaissance, but the period of ice-free open water varies from year to year, subject to the influence of many factors such as strong southerly winds, effects of heat and surging water levels. In addition, the costs of such conventional seafloor investigation are high, and the task is frequently not completed due to adverse ice conditions.
This has led to attempts at site investigations during the Arctic spring when the ice pack is principally a frozen mass of manageable tendencies. With the suitability that the Arctic spring ice pack provides, however, there are still many problems to be overcome. For example, one of prior art attempts may be characterized by the use of a standard surveyor's tripod with an attached towfish which is lowered through a hole made in the ice. From the surface, technicians grip lines which are attached to the towfish and walk in circles to reorient the transducers attached to the towfish. More recently, attempts were made to place a diver on the seafloor holding a towfish as he slowly rotated. Still another attempt consisted of an operation of cutting slots through the ice and towing a side-scan sonar towfish from the ice surface. Highly accurate data cannot be expected from such a towed system which uses a dynamic method with a towed body rolling and pitching. In summary, these prior art operations do not yield acceptably accurate results, and are very costly in both time expended and total resources required.